58 THE FEEDING OF ANIMALS 



stance which does not putrefy and which gives to the 

 tanned hide the properties of leather. Gelatine is much 

 used in various food preparations. 



It is characteristic of the keratins such as hair and horn 

 that they contain a relatively large proportion of sulfur, 

 the analysis of horn and hair showing as high as 5 per 

 cent, the average amount in horn being 3.3 per cent. The 

 keratin bodies serve to give rigidity and wearing quali- 

 ties to certain exterior animal tissues. 



73. Histories, protamines. The proteins in these 

 two groups do not occur as such in nature, and are ob- 

 tained only by separating them from some combination. 

 The two groups are alike in being basic in character 

 and in being found in the spermatozoa of fishes. 

 Histones have also been obtained from the blood cor- 

 puscles of a goose and from the white blood corpuscles 

 of thymus glands. 



CONJUGATED PROTEINS 



74. Nucleo-proteins. These are complex, phosphorus- 

 bearing proteins that sustain an important nutri- 

 tive function. They are regarded as a combination of 

 nuclein with an albumin, the nucleins being compounds 

 of nucleic acid and albumin, and nucleic acid yielding on 

 cleavage phosphoric acid, certain nitrogenous bases known 

 as purins, and a carbohydrate. 



The nucleo-proteins are associated with the nuclei of 

 the cells that make up both plant and animal tissues. 

 They are relatively abundant in glandular tissues such as 

 the spleen, pancreas, thymus gland, and liver. The 

 spermatozoa masses of fishes are especially rich in these 

 compounds. Because certain bases known as purins 



